Racing Suspension - Stock Car Dynamics, Part One

1/11Even with sophisticated test rigs, such as this K&C rig being used by Morse Measurements in Salisbury, North Carolina, racers still must rely on trial and error for the most part, but there is a better way.

We first presented this material in CIRCLE TRACK in early 2003. Since that time we have made reference to bits and pieces of it to illustrate other discussions. The technology presented here represents the greatest leap forward in basic automotive dynamics technology in the last 20 years or so. The basic principles that represent the foundation of this technology were developed some 60 years ago, and what you will read here is a refinement of much of what came later.

When most of us think of the development of racecar dynamics, we may immediately think of the major innovations coming from Indy car racing and/or Formula One. That is a natural conclusion given that they appear to be more sophisticated in design, but the true story is much different. In this particular field of science, stock car racing today is at the head of the class.

2/11Roll centers, or moment centers in reality, and centers of gravity, centrifugal forces, and gravity all have a role to play in determining the desire of the front end of the racecar. We have finally determined the true dynamic effect of these components.

The historical record of the evolution of the knowledge of vehicle dynamics runs directly parallel to the development of the passenger cars and trucks for several understandable reasons. First and foremost, the big automakers had the funds to finance the extensive and expensive research. Also, the need existed to develop better suspension systems for ride comfort as well as drivability. Along with these two "driving" forces also existed the element of competition among automakers which led to the development of more advanced street cars.

The "win on Sunday, sell on Monday" attitude was not restricted to American automakers. Companies such as Ferrari, BMW, Toyota, and Honda, as well as others hold the same to be true. Without racing, the companies would not have had a venue to show the superior quality and the advanced mechanical systems they developed. Consumers relate to and buy winning auto maker's cars.

3/11The Ferrari cars have dominated the past few F1 seasons with numerous wins and Firsts in championship points. Observers of the series noted throughout the past five years that the sleek red Italian cars just flat out handled better than their competition and the McLaren cars are almost equal. So, why is it that the Renault and Honda teams (seventh and nineth in constructor's points to date) cannot match the performance of Ferrari and McLaren in 2008? Could it be they cannot find the dynamic balance? When watching the races and hearing the drivers, handling is a concern. Courtesy of IMS Photo

Stock car racing has always been thought of as the "soap box derby" in all of auto racing. In leading books on the subject of racecar dynamics, stock cars are often referred to as a "particular case" and often referenced by their unpredictable nature associated with handling. It is fairly easy to adjust the handling on an open wheel formula car with wings in the front and rear. A little more downforce at one end will effectively cure a tight (under-steer as it is called in those circles) or loose (over-steer) condition. With the stock car, we do not have such options. The limitations and restrictions imposed by the "stock" chassis' confuse many automotive engineers.

From the 1940s up until the early '90s, no one had defined what comprised a perfect setup for a stock car. For that matter, no one had learned what any racecar wanted for its perfect setup. Setup in all series had largely been developed by trial and error methods, even with the most advanced forms of auto racing.

To better understand and prove why this is true, we need only to take a look at and listen to all of the teams in the top racing series today. In descending order related to how much money is spent for each type of race team we quickly recognize the top contenders. Formula One is far and away number one, NASCAR Sprint Cup is now second, Indy Car racing is third, and U.S. road racing such as the Grand Am DPs and American Le Man Series are fourth and fifth.

A casual observer would, based on the media hype and subterfuge presented, assume that the technology exists that would accurately predict the handling characteristics of the vehicles in each of these top series. But as we listen to the drivers and crews, we find out it does not.

4/11Casey Mears explains what the car is doing, or not doing as the case may be, to crew chief Alan Gustafson. I think what all race teams desire is that perfect balance that will make the car fast and be fast for long periods of time. How often have we seen someone sprint to the front only to drift back several laps later? In Sprint Cup racing, it's still largely trial and error, or what I like to call "reactive engineering." Courtesy of NASCAR

The Ferrari cars have mostly dominated F1 since the year 2002 because they consistently out-handled the competition. At times they were admittedly under-powered, but still turned faster lap times, and that comes from a better handling package. Even new McLaren driver Lewis Hamilton will tell you that he can only drive the car as fast as it wants to go. Fernando Alonso is known as a very good development driver, but not even he can get the once powerful Renault cars up to speed to compete with McLaren and Ferrari, whose cars flat out-handle the others.

It is the same for American based formula cars and Sprint Cup teams. How many times have you heard a SC driver complain of a tight or loose or unpredictable car? It's hit or miss, and whether you're Lewis Hamilton or Tony Stewart, at each race you hope the crew and engineers have guessed correctly.

What has been refined in most top racing series is the hit and mostly miss art of trial and error. Advanced measuring systems are in use today that not only record movements, pressures, and temperatures but also the forces exerted on components. These systems have become useful and necessary tools of the modern day chassis developer. As the teams compile and study all of this information, the fact still remains that they react to, and do not predict, the handling nature of their cars. I call this "reactive engineering" as opposed to "predictive."

5/11Harry Hyde (left) was a crew chief that worked with his own calculations trying to balance his cars. He had his own method worked out and found much success in former Winston Cup racing. He won a lot of races with Bobby Isaac (right), Sam McQuagg, Tim Richmond, and others. Photo by Ken R. Noffsinger

The big news is that technology has evolved and the ability to predict the handling characteristics of your car is available. This information did not come out of any of the major automakers engineering departments nor F1 or Indycar racing. It came from stock car racing and has many times proven itself for over 10 years now.

Developing and refining this technology was a fairly long process and involved many persons, but the "who" is not as important as the "how" and "why?" The answers to those questions begin with a short study of the history of the development of the automobile.

Long before the car, we had horses and wagons. Transportation technology took a quantum leap with the invention of locomotive trains. The first steam powered locomotive was built in 1804 in Wales and was used in mining operations. As the design of trains advanced towards the late 1800s, so did our understanding of powered vehicles. It was inevitable that the automobile would become a vital mode of transportation.

As the auto became more popular, its chassis design became more advanced. The 1903 Ford Model A, the first production automobile, was built much like wagons with leaf spring suspensions similar to the stage coaches of the early days. Power was transferred to the rear wheels via a chain and sprockets. The 1909 Model T incorporated a transmission and drive shaft for the first time and that system is still in use today.

6/11The typical stock car has a front suspension system using double A-arms. These arms are attached to a spindle and the controlling dynamic point is commonly called the roll center although the car rarely rolls around this point. McPherson Strut front suspensions are being used more and more in stock car racing and that system also has a roll center point, similar to the double A-arm system.

The front suspension of that car used one piece spindles attached to the ends of a transverse (sideways to the centerline) leaf spring and used a drag link steering system, similar to the ones used today in many American production and racing stock cars.

Eventually the automakers developed the double A-arm front suspension system using coil springs. That system is the primary system used in stock car racing today.

So, the vehicle we are trying to predict the handling of has a stiff chassis (further strengthened by a roll cage and supports at the front and rear) with a double A-arm, coil spring front suspension, and a solid axle rear suspension with either coil or leaf springs.

The front and rear suspension systems in stock cars are very different from one another both in appearance and in the way they react to the cornering forces that they encounter. Therefore, we must necessarily treat each system independently and try to determine what each one wants to do as the car turns. If we can predict exactly what each desired to do, then we can match the "desires" of both to help create a truly balanced setup.

7/11Roll Axis - Roll couple distribution technology was primarily developed for symmetrical suspension systems such as those found in production automobiles. This method involves calculating the resistance to roll of each suspension system. It does not take into account all of the dynamic effects associated with a race vehicle. An example is the additional roll angle/anti-roll angle created as a result of compression caused by downforce vs. spring split.

Let's go back for a minute and see how chassis technology was progressing through the 1960s to the early '90s. Much of the research was undertaken by the engineers for the automakers, with a heavy influence by the General Motors group.

The primary thread of their analysis of vehicle dynamics involved a model of a vehicle that treated the body and frame as a single unit with a single center of gravity for the sprung mass. The front and rear roll centers were depicted as the points of resistance to lateral forces and were connected by an invisible line or axis and a right angle line between the CG and the "roll" axis. This was the vehicles moment arm.

A moment arm is much like a pry-bar or shovel handle. The CG is equivalent to the end of the bar we hold on to, and the roll centers and axis is the opposite end, where we are applying a force. The longer the bar (moment arm) the more leverage we have and the easier we can move the object, or in this case, roll the car.

In the roll axis thread of technology, each end of the car was calculated to have a given "roll resistance" percentage based on the spring rates and spring base among other factors. In subsequent skid pad testing, a neutral handling car was found to have significantly different roll couple numbers at the front and rear with a heavy emphasis on the front.

8/11The roll angle analysis method allows us to predict how each end of the car wants to react to the force created by cornering. If we know what each end wants to do and can alter the suspension components such as spring rates and roll center locations, then we can design our car to have a balanced setup prior to testing or racing. This is exactly what we shoot for by trial and error guessing. This method saves a lot of time and frustration.

The handling characteristics of the car could be altered by changing the "couple" at each end, but the handling still could not be predicted and was arrived at through trial and error methods. It soon became obvious that the "roll couple distribution" thread of vehicle dynamic analysis did not present a viable method that could accurately predict a stock car's handling performance. Something was obviously missing.

Because technology is universally shared in most cases among automotive engineers in general, we can be fairly sure that up until the early '90s, there did not exist a method that could be used to accurately predict the handling of either an F1 car or a stock car. In my discussions with some of the top race engineers I was led to the same conclusion, a definitive method and associated software did not exist at that time to accurately predict a stock car's handling characteristics.

Then in the early '90s a new method was developed that differed from all previous threads of vehicle dynamic research. It involved treating the vehicle as two separate masses, each with its own separate suspension system and desires.

This method made a lot of practical sense because in a stock car we have two "axles", each supporting their own weight, and each resisting the lateral forces created by cornering. In physics, we are taught that everything is fluid, or somewhat flexible, and dividing the car into separate halves allows us to analyze each one independently to determine its desire.

9/11Using circles to represent the amount of load on each tire, we can visualize weight distribution. With a low static distribution of weight (low cross weight percentage of 48-52 percent), after the weight transfer that occurs during cornering, an ideally balanced setup will have equal load on the left side tires and equal load on the right side tires.

The review of early notes kept by a select few of the top stock car crew chiefs of the '80s and early '90's indicate that they were thinking in the context of a balanced setup and thus the seeds were sown. The goal was to arrange the setup so that the two ends of the car would be balanced in each one's efforts, thereby providing a perfectly balanced and handling car.

Based on these early considerations, in 1994 a method was developed and algorithms (equations and mathmatical calculations) were written that would provide the answers needed to achieve that goal. Weights and measurements from the car and race track were entered into a computer program, and through a series of calculations, a prediction for what each of the two suspension systems desired to do was arrived at. Although the calculations were very complex, the two answers were presented as simple front and rear roll angles.

By treating each end of the car as an independent system removed from the other, we could now accurately calculate and predict what angle each wanted to roll to. The key to developing a balanced setup is to match the desires (roll angles) of each end. So, if the two roll angles are the same, we will have a truly balanced setup.

10/11With a higher static distribution of weight (high cross weight percentage of 56-62 percent), after the load transfer that occurs during cornering, an ideally balanced setup will have equal weight on the right front and left rear pairs of tires and equal weight on the left front and right rear pairs of tires.

There are several critical reasons why a balanced setup is essential to optimum chassis performance. First of all, once balanced, we can accurately predict load transfer. This is the primary reason why the "roll couple distribution" technology failed. An unbalanced car redistributes the load on the four tires in a very unpredictable way. If we cannot determine the desires of each end of the car, balanced or not, we cannot accurately predict the exact amount of load transfer and the resulting loads on each tire.

Secondly, we will have less (almost non-existent) chassis flex with a balanced setup. Compliance, or flexing of the chassis, cannot occur if we remove the forces that cause this to happen. In 1995, I was asked by a prominent race engineer working with a top Cup team what I thought of compliance. I asked if he meant chassis flex, and he replied yes. I told him that if we could remove the forces that ultimately try to twist the chassis, we could mostly eliminate chassis flex. That simple answer astounded him, because no one had approached the problem from that angle.

Last and most importantly, we need to have two sets of tires that are each doing equal amounts of work. Which two are paired depends on the static load distribution. In stock car racing, we will almost never have all four tires doing equal work (having equal load on each tire) under most current left side weight rules. If we can set up the car so that after the load transfers in the corners, we have equal working pairs of tires, then we will have a true balanced setup.

11/11At the recent Charlotte 600 race, Kasey Kahne ran up front all day and eventually won. It appears from this photo that the car is running on the springs and it stayed very consistent. Could it be that the new engineer, Ian Watt, has finally found the mechanical balance needed to bring success to Gillett-Evernham racing? Inside sources say yes. Courtesy of NASCAR

If you carefully watch an F1 or Sprint Cup car going through a turn, you can see the degree of balance that exists. A car that is twitchy or rocks as it turns is not very balanced. The handling may be neutral for the time being, but that does not mean both ends of the car are in sync. A car that loses a lot of speed on a particular run on the same set of tires is not very well balanced. The primary cause of the loss of speed due to an unbalanced setup is because the car's handling balance changes to tight or loose.

Unbalanced setups abuse one or more tires. It is this abuse that causes the tires to wear or heat up excessively. Balanced setups distribute the loads evenly on each pair of tires. This provides maximum traction as well as a consistent handling package.

The advancements that have come from this new approach to chassis setup benefit all of racing. The fact that it came from within the ranks of stock car racing is not hard to understand if you have been around these types of racers for long. They are the most innovative and industrious group that exist in our entire world. The racer digs hard, is not afraid to get his hands dirty to affect change, and when some new technology comes along that proves itself they, as a group, jump on it regardless of what the higher learning institutions continue to teach.

In the next installments we will learn about the specific dynamics of each suspension system and how we can measure and adjust each to find that perfectly balanced setup. These methods have been used in most forms of motor racing around the world.